1. Field of the Invention
The present invention relates to ink-jet heads, methods for driving ink-jet heads, and ink-jet recording apparatuses, in which ink is jetted by applying energy of surface acoustic waves to the ink.
2. Related Background Art
In recent years, research and study have been conducted on nozzleless ink-jet heads utilizing the streaming phenomenon of surface acoustic waves (hereafter also referred to as “SAWs”). A SAW is an elastic wave propagating near the free boundary of a solid and rapidly decaying with depth. The streaming phenomenon of a SAW is a phenomenon that, when a surface acoustic wave that locally propagates in a solid surface is emitted into liquid that is in contact with the solid surface, vibration energy of the surface acoustic wave is propagated into the liquid, and this energy causes minute particles of the liquid to be jetted. An ink-jet head that utilizes the SAW streaming phenomenon can effectively transfer the energy of a surface acoustic wave that is locally induced in the solid surface, and has a substantially greater advantage in view of the energy efficiency compared to other devices that use, for example, bulk vibrations of a piezo element.
However, in the conventional devices, although surface acoustic waves are induced in two directions, only the surface acoustic wave in one direction is used for jetting ink, and the surface acoustic wave in the other direction is treated as being unnecessary and attenuated. For this reason, in view of ink-jetting action, a half of the energy that is converted into the surface acoustic waves is wasted. In addition, a portion of the surface acoustic wave that is unnecessary for jetting ink may reflect on end surfaces of the device and interfere with the part of the surface acoustic wave that is used for jetting ink to thereby disturb the ink-jetting characteristics.
Also, among various research that has been conducted on liquid jetting heads that utilize the SAW streaming phenomenon, technologies concerning the integration of liquid jetting heads are very important in the application and development of this phenomenon to a variety of industrial fields. In one of the head integration technologies, an ink-jet head is provided with a comb-shaped electrode and a plurality of liquid ejection paths, wherein switching between ejection and non-ejection at each of the liquid ejection paths is realized based on whether or not liquid is supplied to each of the liquid ejection paths. However, when piezo elements are employed to conduct switching of the liquid supply to the corresponding liquid ejection paths, there is a limit in improving levels of the integration due to its structural limitation.